ることが

that ...; the fact that ...

→ 居る
phrase Common #4,138
that ...; the fact that ... This is not usually a standalone phrase. The verb before こと is nominalized, and が marks it as the subject. In patterns such as ることがある, it can also contribute to the meaning “sometimes.”
JA: 毎日運動することが大切です。
EN: Exercising every day is important.

トム思ってることが全部顔に出てしまう

Tom wears all his thoughts on his face.

少し違ってることがあるけど、でも私が見たあの

It may be a little different, but… that light I saw.

— アトランティス 失われた帝国 (2001)

気になってることがあって

There’s something that’s been on my mind…

— すずめの戸締まり (2022)

隠してることがあるの

There’s something I’m hiding.